Rechargeable flashlight with integral variable rate battery charger for automotive use

ABSTRACT

A rechargeable flashlight fits into and draws recharging power from an automotive type cigar lighter socket. A thermally controlled charging circuit within the flashlight adjusts the charging rate according to the ambient temperature. When the flashlight is withdrawn from the cigar lighter socket, it is illuminated; when it is replaced it is extinguished. Alternatively, the flashlight may be manually illuminated or extinguished outside the charging socket.

This is a division of application Ser. No. 932,644, filed Aug. 10, 1978U.S. Pat. No. 4,224,658.

BACKGROUND OF THE INVENTION

Battery operated rechargeable appliances usually employ nickel cadmiumrechargeable batteries as a power source. Nickel cadmium batteries canbe recharged many times between use and are not damaged by high-ratedeep discharge. In addition, these batteries are small and can be usedto power relatively large loads.

The permissible charging rate in nickel cadmium batteries varies widelywith temperature. In the vicinity of normal room temperature (20°-35°C.) a typical 1/3AA nickel cadmium battery can be charged at acontinuous overcharge rate of about 30 milliamperes. At low temperaturethe allowable charge rate drops to 2 milliamperes and at hightemperatures of around 65° C., the charging rate drops to about 10milliamperes. Normal household appliances encounter temperatures in the20-35° C. rage and the higher charging rate of 30 milliamperes isappropriate.

The automotive temperature environment has prevented the use ofrechargeable nickel cadmium batteries due to the wide variation inpermissible charging rates required by the great temperature rangesnormally encountered in vehicles, even though an appropriate source ofpower is readily available in the automotive storage battery and itsgenerator or alternator supply.

SUMMARY OF THE INVENTION

The present invention solves the problem of variable permissiblecharging rate of nickel cadmium batteries over the entire range oftemperatures encountered in the outdoor environment. In addition, auseful and convenient rechargeable flashlight is disclosed which isalways kept fully charged and available in the automotive cigar lighter.The rechargeable flashlight is automativally illuminated by the act ofremoving it from the cigar lighter and is extinguished by the act ofreplacing it in the cigar lighter.

The present invention employs a temperature controlled charging networkwhich maintains the charging current to a nickel cadmium battery withinthe permissible range. A matched pair of thermistors comprising anegative temperature coefficient (NTC) and a positive temperaturecoefficient (PTC) thermistor are placed in series between the automotivebattery and the nickel cadmium battery during charging. The sum ofresistances placed in series with the nickel cadmium battery varies withtemperature such that the minimum resistance occurs in the roomtemperature region of between 20° and 35° C. and the resitance increaseson each side of the minimum. The current passing through the thermistornetwork consequently reaches a peak within the maximum permissiblecharging current at the temperature of minimum resistance in thethermistor network and falls off on either side thereof at values whichcontrol the charging rate within the acceptable region throughout theentire range of possible temperatures.

The thermistor network, battery and lamp are contained in a case whichforms a plug suitable for fitting into and drawing power from aconventional cigar lighter in an automotive vehicle. A switch within theflashlight is actuated into the charging position by the pressureemployed to force the flashlight into the cigar lighter socket. In thecharging position, the thermistor network is placed in series betweenthe power source on the vehicle and the nickel cadmium battery. When theflashlight is removed from the cigar lighter socket, the force necessaryto remove it operates the switch into the on position removing thethermistor network from connection with the battery and, instead,connecting the lamp and battery in series. Consequently, when theflashlight is removed from the cigar lighter socket, the lamp isilluminated. When the flashlight is pressed into the cigar lightersocket, the lamp is extinguished and the charging circuit isestablished. The lamp can also be manually illuminated or extinguishedexternal to the cigar lighter socket by manipulating the plug ratherthan by removing or inserting the flashlight in the cigar lightersocket.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a rechargeable flashlight according to the presentinvention withdrawn from its socket and illuminated.

FIG. 2 shows a rechargeable flashlight according to the presentinvention inserted into its socket and extinguished.

FIG. 3 shows a cross section of a rechargeable flashlight according tothe present invention in the condition for illumination of the lamp.

FIG. 4 shows a cross section of a rechargeable flashlight according tothe present invention arranged for charging of the rechargeable battery.

FIG. 5 shows a schematic diagram of the rechargeable flashlightaccording to the present invention as well as an automotive battery towhich it may be connected.

FIG. 6 shows a simplified diagram of the rechargeable flashlightconnected for illumination of the lamp.

FIG. 7 shows a simplified schematic diagram of the rechargeableflashlight according to the present invention connected for rechargingfrom an automotive battery.

FIG. 8 shows a curve of maximum allowable charging rate versus batterytemperature.

FIG. 9 shows a curve of resistance versus temperature for an NTCthermistor.

FIG. 10 shows a curve of resistance versus temperature for a PTCthermistor.

FIG. 11 shows a curve for resistance versus temperature for a seriescombination of PTC and NTC thermistors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 there is shown generally at 10 a rechargeableflashlight according to the present invention. The rechargeableflashlight 10 enclosed within a case is shown withdrawn from a cigarlighter socket 12 of a type well known in the art.

A shell 14 on the rechargeable flashlight 10 is adapted to slide intothe cigar lighter socket 12 with considerable friction as isconventional in cigar lighter applications. An end cap 16 is located atthe inner extremity of the rechargeable flashlight 10 and makeselectrical contact with one terminal within the cigar lighter socket 12.The contact of the shell 14 with the inside of the cigar lighter socketprovides a second electrical contact.

A ring 18 at the outer end of the rechargeable flashlight 10 isconnected thereto by a slide tube 20. A lamp 22 which is appropriate tothe voltage and power capability of a nickel cadmium battery is locatedin the forward end of the ring 18.

When the rechargeable flashlight 10 is withdrawn from the cigar lightersocket 12 by grasping the ring 18 and applying force in the directionshown by the arrow 24, the slide tube 20 attached to the ring 18 ispulled partway out from the shell 14 due to the frictional fit betweenthe shell 14 and the cigar lighter socket 12. This causes the lamp 22 tobecome illustrated and causes the charging circuit to be disconnected aswill be explained.

Referring now to FIG. 2, the rechargeable flashlight 10 is showninserted into the cigar lighter socket 12. When force is applied to thering 18 to insert the rechargeable flashlight 10 into the cigar lighersocket 12 against the frictional resistance between the shell 14 and thecigar lighter socket 12 in the direction shown by the arrow 26, theslide tube 20 is moved inward into the shell 14 and the ring 18 is movedcloser to the shell 14. This causes the lamp 22 to become extinguishedand the charging circuit, described later, to become engaged.

Referring now to FIG. 3, there is shown the rechargeable flashlight 10arranged for illumination of the lamp 22. A battery 28 preferably arechargeable nickel cadmium battery of the type having a metallic shell30 covering the perimeter and one end and a metallic contact 32 at theother end is disposed in the interior of the slide tube 20. The metallicshell 30 at the end 34 of the battery 28 is pressed upward againstterminal 36 of the lamp 22. A spring 38 presses upward on metalliccontact 32 to maintain the battery in position and to provide electricalcontact thereto. An insulating tube 82 covering the perimeter of thebattery 28 prevents contact between the metallic shell 30 and the insideof the slide tube 20.

A serpentine lower spring 40 is connected to the spring 38 by anintermediate metallic portion 42. The serpentine lower spring 40 has alamp contact 44 which, in the position shown, is pressed against thebottom 46 of the slide tube 20. The serpentine lower spring 40 also hasa charging contact 48.

An opening 50 is axially located in the bottom 46 of slide tube 20. Anactuator 52 aligned with the opening 50 has a generally cone-shaped head54. The actuator 52 is retained in an insulating body 56 by a collar 58and a washer 60.

The lower end 62 of the actuator 52 is in electrical contact with oneterminal of a negative temperature coefficient thermistor 64. The secondterminal of the NTC thermistor 64 is in contact with one terminal of apositive temperature coefficient thermistor 66. The second terminal ofthe PTC thermistor 66 is in contact with one side of a resilientconductive spacer 68. The second side of the conductive spacer 68 is incontact with the bottom 70 of end cap 16. The conductive spacer 68 takesup any manufacturing tolerances in the thermistors and the actuator toensure a good electrical conducting path between the cap 16 and theactuator 52. The conductive spacer 68 may be a resilient mass such asconductive rubber or plastic or it may be a metallic spring to providean upward resilient bias urging the thermistors 64, 66 against thewasher 60. As shown, the PTC and NTC thermistors 66, 64 are electricallyin series between the end cap 16 and the actuator 52.

At its upper end, the slide tube 20 is electrically connected to a lampcarrier 72 having a threaded socket 74 centrally located therein. Thelamp 22 has a threaded barrel 76 about its circumference which is shownin threaded mesh with the threaded socket 74.

A flange 78 on the slide tube 20 makes electrical contact with lampcarrier 72. A clamp ring 80 holds the lamp carrier 72 and flange 78 inthe ring 18. Therefore, when the ring 18 is pulled or pushed in theaxial direction, a corresponding axial force is applied to the slidetube 20 to force it into or pull it out of the shell 14.

The slide tube 20 fits into a plastic tubular housing 84. A tang 86 onthe slide tube 20 angles outward and engages an abutment 88 in theplastic tubular housing 84 to positively limit the outward motion of theslide tube 20 from the plastic tubular housing 84.

A spring member 90 of a type well known in the art provides a resilientconductive biasing force between the inside of the shell 14 and theoutside of the slide tube 20. The spring member 90 provides electricalcontinuity between the shell 14 and the slide tube 20 at all times. Inaddition, the frictional resistance provided by spring member 90 tendsto maintain the slide tube 20 in whichever position it is placed.

In the condition shown, a continuous electrical circuit is formed frommetallic contact 32 on battery 28 through spring 38, serpentine lowerspring 40, lamp contact 44 between serpentine lower spring 40 and thebottom 46 of slide tube 20, lamp carrier 72, threaded barrel 76,filament in the lamp 22 (not shown), and through terminal 36 of the lamp22 to the end 34 of the battery 28. This continuous circuit causes thelamp 22 to be illuminated.

Referring now to FIG. 4, there is shown the rechargeable flashlight 10of the present invention arranged for charging of the battery 28. Therechargeable flashlight 10 is arranged for charging by being insertedinto a standard cigar lighter socket partially represented in FIG. 4 bythe positive contact 92 contacting the end cap 16 and the negativecontact 94 contacting the shell 14. The positive contact 92 is connectedto the positive terminal of the schematically shown automotive battery96, and the negative contact 94 is connected to the negative terminal ofthe automotive battery 96.

The act of insertion of the rechargeable flashlight 10 into the cigarlighter socket 12 involves pressing inward on ring 18. This results inslide tube 20 sliding inward into the plastic tubular housing 84 untilthe bottom 46 of the slide tube 20 is stopped by abutment surface 98 oninsulating mass 56. As the tube 20 is slid into the plastic tubularhousing 84, the actuator 52 engages charging contacts 48 of theserpentine spring 40 and thus lifts lamp contact 44 out of conductiveengagement with the bottom 46 of slide tube 20. This breaks the lampillumination circuit and thus extinguishes the lamp. A charging circuitis formed from the automotive battery 96 to the battery 28 by way ofpositive contact 92, end cap 16, conductive spacer 68, positivetemperature coefficient thermistor 66, negative temperature coefficientthermistor 64, actuator 52, charging contact 48, serpentine spring 40,spring 38, metallic contact 32 of battery 28, end 34 of battery 28,contact 36 of lamp 22, the lamp filament (not shown), threaded socket74, lamp carrier 72, slide tube 20, metallic spring member 90, shell 14,and negative contact 94 back to the negative terminal of the automotivebattery. The rechargeable battery 28 is thereby connected for rechargethrough the two thermistors 66 and 64 and the lamp filament. Thecharging current in the circuit is insufficient to illuminate the lampfilament during charging. The lamp filament therefore merely acts as asubstantially constant series resistance in the charging circuit.

Referring now to FIG. 5, there is shown a schematic diagram of therechargeable flashlight 10 showing the switching method for illuminationand charging wherein the reference numerals are the same for similarparts as described in connection with previous figures. The single-poledouble-throw switch 100 is formed by actuator 52, bottom 46 of slidetube 20 and serpentine spring 40. When in the charging position shown infull line, SPDT switch 100 connects the two thermistors 64, 66 in serieswith the automotive battery 96, the rechargeable battery 28 and the lamp22. When in the lamp on condition shown in dashed line, switch 100disconnects the thermistor network 64, 66 and connects the positiveterminal of the rechargeable battery 28 directly to the lamp 22 tobecome illuminated.

The simplified schematic diagram in FIG. 6 shows the illuminationcircuit, established as in FIGS. 1 and 3. The battery 28 and lamp areconnected in parallel.

The simplified schematic diagram in FIG. 7 shows the charging circuitestablished as in FIGS. 2 and 4. The positive terminal of automotivebattery 96 is connected through thermistors 66 and 64 to one terminal ofrechargeable battery 28. The negative terminal of automotive battery 96is connected through lamp 22 to the other terminal of rechargeablebattery 28.

It would be clear to one skilled in the art that the sequence ofcomponents in the charging circuit of FIG. 7 is immaterial. The twothermistors 64, 66 and the lamp can be permuted and transposed withoutany effect on circuit function.

The arrangement of FIGS. 3 and 4 in which the two thermistors 64, 66 bein close proximity has the disadvantage that heat generated by one ofthe thermistors can influence the other thermistor. It may be preferableto thermally separate the two thermistors 64, 66 from each other toreduce this effect and, in fact, this is the preferred embodiment.Furthermore, it is desirable that the thermistors 64, 66 follow thetemperature of the battery 28. The invention also contemplates placingthe thermistors 64, 66 into close thermal contact with the rechargeabebattery 28 to accomplish this. Thermal isolation between the twothermistors can be improved by placing the two thermistors at oppositeends of the rechargeable battery 28.

FIG. 8 shows the permissible charge rate for a particular nickel cadmiumbattery of the type manufactured by General Electric Corporation underthe identification XKCF 100 ST for varying battery temperature. It isnoted that the maximum permissible charging rate of 30 milliamperesoccurs in the vicinity of 28° C. and decreases on either side of 28° C.

The resistance of an NTC thermistor versus temperature is shown in FIG.9. The resistance of a PTC thermistor versus temperature is shown inFIG. 10. The sum of the resistances of the PTC and NTC series network isshown in FIG. 11.

Although other battery and lamp arrangements may require otherthermistor characteristics, the following specific thermistors were usedin one embodiment reduced to practice:

NTC thermistor--MCI Part No. T1084

PTC thermistor--MCI Part No. P57171

With the combination previously described, a rechargeable flashlight 10according to the present invention can be charged from a 12 voltautomotive battery source over the range of ambient temperaturesnormally encountered in automotive applications without danger ofbattery damage due to excessive charge rate at any temperature. Thecombined network resistance shown in FIG. 11 when placed in series withthe fixed resistance of the lamp 22 provides a limit to the maximumcharging rate within the limits shown in FIG. 8 for all batterytemperatures.

It would be clear to one skilled in the art that various changes couldbe made in the present invention without departing from the spirit andscope of the invention. For example, two or more rechargeable batteries28 could be connected in the series in the flashlight to permit longerdischarge time or brighter lamp. This would require a change in thevalues of the NTC and PTC thermistors to control the charging rate. Oneskilled in the art would be capable of selecting appropriate thermistorsand other components from those readily available on the commercialmarket without any experimentation whatsoever in the light of thepresent specification. Similarly, a charging path to the battery 28could be established which eliminates the lamp filament in series withthe charging path. This would again require an adjustment in thespecifications of the two thermistors according to principles well knownby those skilled in the art. Other types of batteries, including NickelCadmium and others, may require a different relationship betweenchanging rate and environmental variables.

It will be understood that the claims are intended to cover all changesand modifications of the preferred embodiments of the invention, hereinchosen for the purpose of illustration which do not constitutedepartures from the spirit and scope of the invention.

I claim:
 1. In a rechargeable flashlight, a switching devicecomprising:(a) a housing; (b) a sliding member in said housing, saidsliding member being electrically conducting; (c) said sliding memberbeing movable between a first and second position; (d) means forelectrically connecting said sliding member into an electrical lampcircuit; (e) a rechargeable battery in said housing, said rechargeablebattery having two terminals, one of said terminals being electricallyconnected into said electrical lamp circuit; (f) anelectrically-conducting actuating member fixed in said housing; (g) saidactuation member being electrically insulated from said sliding member;(h) means for electrically connecting said actuating member to abattery-charging means; (i) a spring having two ends, said springpositioned between said actuation member and said rechargeable batteryso as to be moved from a first position to a second position by saidelectrically conducting actuating member when said sliding member ismoved from said first position to said second position; (j) one end ofsaid spring is electrically connected to the other terminal of saidrechargeable battery; (k) the other end of said spring is biased intoelectrical contact with said sliding member when said sliding member isin said first position; and (l) said spring being lifted from electricalcontact with said sliding member by mechanical and electrical contactwith said actuating member when said sliding member is in said secondposition.
 2. The switching device of claim 1 wherein said sliding memberis a sliding tube holding said rechargeable battery, said rechargeablebattery being electrically insulated from said sliding tube.
 3. Theswitching device of claim 1 wherein said battery-charging meanscomprises a charging network including anegative-temperature-coefficient and thermistor and apositive-temperature-coefficient thermistor in series, said thermistorscontributing sufficient resistance to limit charging current topredetermined values at all temperatures.
 4. The switching device ofclaim 1 wherein said housing forms a plug suitable for fitting into andmaking electrical connection with an automotive cigar lighter socket. 5.In a rechargeable flashlight, a switching device operative to changesaid rechargeable flashlight between an illuminating mode and a chargingmode in a charging network therein comprising:(a) a housing; (b) anelectrically conductive slide tube in said housing, said slide tubeholding said rechargeable battery and said lamp, said rechargeablebattery being electrically insulated from said slide tube; (c) saidslide tube having first and second positions in said case; (d) said lamphaving two terminals; (e) said rechargeable battery having twoterminals, one of said terminals of said rechargeable battery being inelectrical contact with one terminal of said lamp; (f) the remainingterminal of said lamp being in electrical contact with said slide tube;(g) a spring in contact with said second terminal of said battery; (h)said spring having a lamp contact; (i) said spring having a chargingcontact; (j) an actuator positioned in said case to move said springfrom a first position to a second position when said slide tube is movedfrom said first position to said second position; (k) said actuatingmember being electrically conducting; (l) means for connecting saidactuating member into said charging network; (m) said spring in saidfirst position of said slide tube being biased to contact said slidetube at said lamp contact; and (n) said actuator in a second position ofsaid slide tube lifting said spring from contact with said slide tubeand contacting said spring at said charging contact.
 6. In arechargeable flashlight of the type for insertion into an automotivecigar lighter socket for charging of said rechargeable flashlighttherein, a switching device operative to place said flashlight in thecharging mode upon insertion into said automotive cigar lighter socketcomprising:(a) a housing, said housing forming a plug suitable forfitting into and making electrical connection with an automotive cigarligher socket; (b) a sliding tube in said housing, said sliding tubebeing electrically conducting; (c) said sliding tube being movablebetween a first and second position, said sliding tube being in saidsecond position when said housing is fitted into said automotive cigarlighter socket; (d) means for electrically connecting said slidingmember into an electrical lamp circuit; (e) a rechargeable battery insaid housing, said rechargeable battery having two terminals, one ofsaid terminals being electrically connected into said electrical lampcircuit; (f) an electrically-conducting actuating member fixed in saidhousing; (g) said actuation member being electrically insulated fromsaid sliding member; (h) means for electrically connecting saidactuating member to a battery-charging means; (i) a spring having twoends, said spring positioned between said actuation member and saidrechargeable battery so as to be moved from a first position to a secondposition by said electrically conducting actuating member when saidsliding member is moved from said first position to said secondposition; (j) one end of said spring is electrically connected to theother terminal of said rechargeable battery; (k) the other end of saidspring is biased into electrical contact with said sliding member whensaid sliding member is in said first position; and (l) said spring beinglifted from electrical contact with said sliding member by mechanicaland electrical contact with said actuating member when said slidingmember is in said second position.